Described below is an actuator for a valve, in particular for a valve of a heating, ventilation and/or air conditioning system.
In many applications in the field of heating, ventilation and air conditioning (HVAC) technology, a heat transfer medium is used in order to transfer thermal energy from a source location to a destination location. The transfer of thermal energy can serve the purpose of heating a room or a zone within a building. In this case the heat transfer medium absorbs thermal energy at the source location and releases at least part of it again after being conveyed to the destination location. Equally, the transfer of thermal energy can also serve to cool a room or a zone within a building. In this case the heat exchange medium absorbs thermal energy at the destination location and releases at least part of it again at the source location.
The heat transfer medium can be any desired fluid. Water is used in most cases. Water has the advantage that it has a high specific thermal capacity and therefore can convey a particularly great heat flow volume per unit mass.
Valves, also known as HVAC valves, are used in order to control or regulate the flow of heat transfer medium in an HVAC system. For example, the flow rate of the heat transfer medium can be varied by what is termed a cutoff or restrictor valve. Suitable mixing of the heat transfer medium at a specific temperature level with a heat transfer medium at a different temperature level can be realized by a multiway valve and as a result the heat output capacity can be varied.
HVAC valves have an actuator which in principle can be driven or, as the case may be, adjusted by way of different types of actuators. (A) A first type of actuator is, for example, a motor which, when provided with suitable control, permits an automatic adjustment of the valve. (B) A second type of actuator is a manual adjustment mechanism, a handwheel for example, with which an operator can manually adjust the HVAC valve in question. The possibility of manual adjustment can be of advantage in particular when an HVAC system is put into operation for the first time. (C) Constituting a third type of actuator is what is termed a return spring, which, after the HVAC valve has been adjusted by a manual adjustment mechanism and/or a motor, automatically resets the HVAC valve to its starting position, after a power outage for example. As well as the aforementioned actuator (A), an HVAC valve typically has in addition the aforementioned actuator(s) (B) and/or (C). Various actuators are available for HVAC valves, these being briefly explained below:
Non Spring Return (NSR) actuators: This type of valve actuator has a motor and a manual adjustment mechanism. No return spring is present, so NSR actuators are also called non-spring return actuators.
With Spring Return (WSR) actuators: This type of valve actuator has as its possible energy sources a motor, a return spring and a manual adjustment mechanism. A WSR actuator is normally driven by the motor in what is termed auto mode. However, if a supply voltage for the motor fails, the valve driven by the actuator is closed by the return spring. If no supply voltage is present at the motor, the WSR actuator can be opened manually and locked in any desired position. As soon as the supply voltage is applied once more, the WSR actuator is unlocked again and the WSR actuator switches over to normal auto-mode operation.
Technischer Überwachungs-Verein (TÜV) Spring Return (TSR) actuators: Valve actuators of this type, which are also referred to as spring return actuators, have a motor and a return spring as possible energy sources. Owing to TÜV (Germany's Technical Inspection Authority) standards that are to be complied with for certain applications, TSR actuators must not have any manual adjustment mechanism. In the event of a power outage the return spring automatically closes the HVAC valve coupled to the TSR actuator.
Actuators for HVAC valves must have a number of technical characteristics and/or fulfill a number of technical requirements in order to be used for HVAC systems in real-world applications. Thus, for example, depending on operating mode, a suitable actuator must be able to switch one of the three energy sources “motor”, “return spring” and “manual adjuster” to a movable restrictor element of an HVAC valve.
Furthermore, the torque which can act on the valve or on a gearing mechanism of the actuator by the manual adjustment mechanism should be limited by a suitable overload clutch so that intentional and/or accidental damage to actuator and/or valve can be prevented. However, known torque-limiting devices for HVAC valves are technically relatively complex, and inflexible besides, since a predetermined maximum torque to be transmitted cannot be varied.